The reproductive system of model species such as the domestic cat and its non-domestic wild relatives offer an unusual opportunity for understanding the changes and adaptations of genes that mediate species isolation and survival. The LGD has undertaken a comparative physiology approach to describe the aspect for feline reproduction that discriminates between species and allows for behavior co-adaptation. In addition, empirical methods to develop cryopreservation have been assessed to optimize assisted reproductive technologies in these species, including artificial insemination, in vitro fertilization and embryo transfer between these closely related species. Models of how to use new technologies to assess reproductive fitness are emerging to help insure gene diversity and even propagate endangered species. Non-invasive hormone metabolite monitoring, artificial insemination and genome resource banking are being optimized to describe the adaptive differences among the Felidae. Significant discoveries include the discovery that standard cooling techniques for cat sperm result in extensive cell membrane damage, allowing the creation of slower, more effective cooling procedures. Sperm from males producing many malformed cells are less likely to survive a cooling-freezing-thawing stress. Egg freezing studies reveal that cat eggs are highly sensitive to cool temperatures. Investigations also continue on the transmission of feline immunodeficiency virus (FIV) (related to human immunodeficiency virus, HIV) in cat semen. A related challenge is the high incidence of abnormally shaped sperm found in the semen of some domestic cats and many endangered cat species. This condition, known as teratospermia and common in men, limits fertilization capacity. Although sperm from teratospermic cats were found this year to have the same amount of DNA as normal males, the former have decreased amounts of protamine, a class of nuclear proteins that play an important role in DNA stabilization. Animal Models for AIDS